1. Field of the Invention
The present invention relates generally to the fields of hormone receptors and drug design. More particularly, it concerns the androgen receptor, methods for regulating androgen receptor gene expression, rational drug design through specific antisense and antigene technology, and also provides specific compositions, including pharmaceutical agents, for use in inhibiting the expression of the androgen receptor gene and treating related pathologies such as prostatic hypertrophy and androgenetic alopecia.
2. Description of the Related Art
Regulated function of hormonal agents play a critical role in health and disease. Target cell responsiveness to a hormonal signal is a product of both the cellular concentrations of the hormone ligand and the actions of its specific receptor protein. Disease conditions such as androgen-dependent prostatic hypertrophy and neoplasia are a result of the aberrant actions of steroid hormones. The design of drugs for the treatment of these conditions is now feasible through the use of modified steroid ligands that act either as receptor agonist/antagonist or as enzyme inhibitors. However, a major problem inherent to `receptor-fitting` drug design is cross-reactivity of the ligand agonist/antagonist to related receptors and the consequent side effects.
The androgen receptor (AR) is a member of the ligand-dependent transcription factor superfamily. The ligand-dependent transcription factor superfamily includes, the steroid hormone receptors, the thyroid hormone/retinoid/vitamin D receptors, the receptors for certain xenobiotic agents and related orphan receptors (Evans, 1988; O'Malley, 1990; Isseman & Green, 1990). Information on the regulation of most of the steroid receptor genes, including the gene for AR, is rather sparse (Baarends et al., 1990; Tilley et al., 1990; Encio et al., 1992; Huckaby et al., 1987; Leclerc et al., 1992). Delineation of upstream regions and transcriptional factors that regulate the expression of the androgen receptor gene will narrow this gap, and aid in understanding the interplay of various transcription factors in tissue-specific expression of the AR gene.
The androgen receptor (AR) gene is expressed at high levels in various reproductively relevant cell types, and plays a pivotal role in the development and maintenance of sex functions. The AR gene is also expressed in many non-reproductive tissues including brain, liver, kidney and bone marrow (Milin & Roy, 1973; McEwen, 1980; Pajunen et al., 1982; Colvard et al., 1989; Song et al., 1992). The AR regulates a number of enzymes and proteins in both reproductive and non-reproductive tissues. Aberrant regulation of the AR gene is associated with reproductive abnormalities such as the androgen insensitivity syndromes. Abnormal regulation of the androgen receptor gene is also believed to be important in prostatic hypertrophy and neoplasia (Pinsky & Kaufman, 1987; Coffey & Pienta, 1987; Yarbrough et al., 1990; Newmark et al., 1992).
The etiology of androgen dependent alopecia has also been traced to androgen dysfunction (Neil S. Sadik and Donald Charles Richardson, Your Hair, Helping to Keep It, Consumer Reports Books, editors and publishers, Yonkers, N.Y., 1992). Androgenetic alopecia, also known as male pattern baldness, is observed in both men and women, and is statistically the most common form of hair loss in men. Commercial preparations for controlling hair loss occupy a large market in the United States, with several billion dollars spent annually on hair loss prevention treatments. Rogaine.RTM. is a prescription preparation currently used to prevent hair loss and includes the active ingredient, minoxidil. This treatment controls hair loss primarily by enhancing blood circulation to the treated area. However, limited success with such agents has been reported.
Relatively little is known regarding the regulation of AR gene expression or function. The sequence of the androgen receptor complementary DNA has been determined (Lubahn et al. (1988) and Chang et al. (1988)). Marcelli et al. (1990) have demonstrated a correlation between a defect at position 772 of the androgen receptor gene and decreased androgen receptor gene and mRNA function. However, the sequence for the AR gene promoter has not been characterized beyond nucleotide position -570, and no specific upstream promoter regions or binding sites for transcription factors have been demonstrated.
The promoter regions of eukaryotic genes generally contain polypurine/polypyrimidine regions that are the preferred sites for the binding of transcription factors. Polypurine-polypyrimidine stretches are also candidates for triple helix formation with single-stranded oligonucleotides through Hoogsteen base pairing (Durland et al., 1992). Formation of a triple helix disrupts the upstream interaction of transcriptional factors thereby affecting gene expression. Oligonucleotide directed modulation of gene transcription by triple helix forming oligonucleotides (TFOs) is a feasible method for attenuating several genes with important regulatory functions such as c-myc, EGF receptor and interleukin-2 receptor (Durland et al., 1992; Bino et al., 1993; Grigopiev et al., 1992).
The lack of specificity prevalent in receptor-fitting approaches can potentially be overcome by antisense nucleic acid drug design directed at promoter regions. Antisense nucleic acids may take the form of small oligonucleotides that enter cells through, for example, receptor mediated endocytosis. This approach offers the advantage of being highly specific and relatively non-toxic even at very high concentrations. Use of these technologies has not been applied to regulating androgen receptor gene expression, or in pathologies that relate to the expression of the androgen receptor gene, such as prostatic hypertrophy and androgenetic alopecia.
The lack of knowledge of steroid receptor gene promoter sequences has prevented the realization of the enormous potential of screening and treatment techniques related to altered function of the androgen receptor gene. The identification of critically important regions of the androgen receptor gene promoter would provide information useful in the development of potent and specific oligonucleotide and antisense screening techniques and therapies not currently available.